1. Field of the Invention
The present invention relates to an internal combustion engine equipped with a variable valve controlling system and to a motorcycle on which the internal combustion engine is mounted.
2. Description of the Background Art
There has been a conventional internal combustion engine (also referred to as an engine) designed to switch the valve actions by use of a rocker arm. The rocker arm is disposed to link an engine valve with first and second cams that serve the engine valve and is supported by a rocker-arm shaft swingably and slidably in the axial direction of the rocker-arm shaft. By sliding on the rocker-arm shaft in the axial direction, the rocker arm engages selectively with one of the two cams to switch the valve actions (see, for example, Patent Document 1).
The variable valve controlling system of Patent Document 1 includes a single actuator (diaphragm) to activate rocker arms. The actuator is disposed in a cylinder head on one side where one ends of a pair of rocker-arm shafts are arranged. A rod extends in a stoke direction of the actuator, and a leading end member of the rod slides the rocker arms on the pair of rocker-arm shafts.    [Patent Document 1] JP-A-58-190507
In the above-described conventional configuration, however, some arrangement of the rocker-arm shafts makes it difficult to activate the rocker arms with the single actuator. Providing plural actuators, however, will increase significantly the number of component parts.
An object of the present invention, therefore, is to provide an internal combustion engine equipped with a variable valve controlling system in which a single actuator to activate the rocker arms is disposed in a cylinder head on one side where one ends of the rocker-arm shafts are disposed, while enabling the single actuator to activate the rocker arms irrespective of the arrangement of the rocker-arm shafts. Another object of the present invention is to efficiently arrange the actuator in a motorcycle on which the internal combustion engine is mounted.